This application is based on patent application Ser. No. 2000-128482 filed Apr. 27, 2000 in Japan, the content of which is incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to a registration adjusting method for correcting a mounting error of printing heads by controlling a printing timing between a plurality of printing heads in an ink-jet printing apparatus performing printing on a printing medium using the printing heads.
2. Description of the Related Art
In a serial type printing apparatus employing a serial scanning system taking a direction substantially perpendicular to a feeding direction of a printing medium (auxiliary scanning direction) as a primary scanning direction, printing for the entire printing medium is performed by repeating operations of printing (primary scan) an image by printing heads mounted on a carriage moving along the printing medium, after printing for one line, performing paper feeding for a predetermined amount, and subsequently performing printing (primary scan) again for the next line for the printing medium.
In such ink-jet type color printer of the type performing serial printing, a plurality of printing heads respectively ejecting inks of yellow, magenta, cyan and black are mounted on the carriage. Upon primary scan, respective colors of inks are ejected from respective of a plurality of printing heads at predetermined timing to perform image printing.
Upon performing color printing with the construction set forth above, images of respective colors formed by a plurality of printing heads have to be accurately overlaid per each pixel in order to maintain good image quality. For this purpose, it is required to accurately adjust positional relationship of a plurality of printing heads.
However, upon exchanging the printing head and so on, if the positional relationship of a plurality of printing heads on the carriage is displaced, desired printing quality cannot be obtained. In order to solve this problem, the following registration adjustment is performed.
Namely, using a plurality of printing heads, a registration error detecting chart pattern is printed. The result of printing is read by a sensor or the like to detect offset amounts of depositing positions between respective printing heads on the basis of the result of reading. Upon printing, on the basis of the detected offset amount, ejection timing of each printing head is adjusted to have dots of respective colors overlaid at the same position.
However, in the printing apparatus, in which a plurality of printing heads are aligned in the scanning direction, it is difficult to appropriately perform registration.
The present invention has been developed in view of the shortcoming set forth above. Therefore, it is an object of the present invention to reduce registration adjustment due to tolerance in manufacturing of a linear encoder scale, thereby improving image quality.
It is another object of the present invention to provide a registration adjusting method of an ink-jet printing head which can effectively perform the process upon exchanging a reference head.
In the first aspect of the present invention, there is provided a registration adjusting method for an ink-jet printing apparatus, in which one of a plurality of printing heads arranged along a primary scanning direction is taken as a reference printing head, a relative positional relationship between an ink droplet ejected on a printing medium from the reference printing head and an ink droplet ejected on the printing medium from a non-reference printing head is measured by converting number of encoder pulse signals, and registration adjustment for nonreference printing head is performed by correcting an ink ejection timing of the non-reference printing head relative to the reference printing head with the encoder pulse signals on the basis of a result of measurement,
wherein a printing head located close to a center position among the plurality of printing heads is taken as the reference printing head for registration adjustment.
With the present invention as set forth above, the printing head located at a position closest to the center position among a plurality of printing heads is taken as a reference for registration adjustment. Therefore, distances between respective non-reference printing heads and the reference printing head can be equalized so that a non-reference printing head having a particularly large distance from the reference printing head in comparison with other non-reference printing heads can be eliminated. Accordingly, an error in registration adjustment due to tolerance in manufacturing of the linear encoder scale can be reduced.
In the second aspect of the present invention, there is provided a registration adjusting method for an ink-jet printing apparatus, in which one of a plurality of printing heads arranged along a primary scanning direction is taken as a reference printing head, a relative positional relationship between an ink droplet ejected on a printing medium from the reference printing head and an ink droplet ejected on the printing medium from a non-reference printing head is measured by converting the number of encoder pulse signals, and registration adjustment for the non-reference printing head is performed by correcting an ink ejection timing of the non-reference printing head relative to the reference printing head with the encoder pulse signals on the basis of a result of measurement, wherein, upon exchanging the reference printing head, the method comprises the steps of:
exchanging the reference printing head on a carriage;
ejecting ink on the printing medium from the reference printing head in a condition where the carriage is scanned to a predetermined first position;
ejecting ink on the printing medium from a predetermined non-reference printing head in a condition where the carriage is scanned to a second position from the predetermined first position for a distance corresponding to a distance between the reference printing head and the predetermined non-reference printing head;
measuring a depositing position error between two strings of ink ejected on the printing medium; and
correcting the ejection timing of the reference printing head on the basis of the measured depositing position error so that the two strings of ink match in the primary scanning direction.
With this invention, when the reference printing head is exchanged, the registration adjustment of the reference head is performed using registration adjustment amount data of the non-reference printing head and the exchanged reference head to make registration adjustment upon exchanging of the reference printing head efficient and whereby a period for registration adjustment is shortened.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.